Dietary interventions for maintaining cognitive function in cognitively healthy people in mid life

Plant Foods Rich in Antioxidants and Human Cognition: A Systematic Review

Oxidative stress can compromise central nervous system integrity, thereby affecting cognitive ability. Consumption of plant foods rich in antioxidants could thereby protect cognition. We systematically reviewed the literature exploring the effects of antioxidant-rich plant foods on cognition. Thirty-one studies were included: 21 intervention, 4 cross-sectional (one with a cohort in prospective observation as well), and 6 prospective studies. Subjects belonged to various age classes (young, adult, and elderly). Some subjects examined were healthy, some had mild cognitive impairment (MCI), and some others were demented. Despite the different plant foods and the cognitive assessments used, the results can be summarized as follows: 7 studies reported a significant improvement in all cognitive domains examined; 19 found significant improvements only in some cognitive areas, or only for some food subsets; and 5 showed no significant improvement or no effectiveness. The impact of dietary plant antioxidants on cognition appears promising: most of the examined studies showed associations with significant beneficial effects on cognitive functions-in some cases global or only in some specific domains. There was typically an acute, preventive, or therapeutic effect in young, adult, and elderly people, whether they were healthy, demented, or affected by MCI. Their effects, however, are not attributable only to anti-oxidation.

Computerised cognitive training for 12 or more weeks for maintaining cognitive function in cognitively healthy people in late life

BACKGROUND

Increasing age is associated with a natural decline in cognitive function and is the greatest risk factor for dementia. Cognitive decline and dementia are significant threats to independence and quality of life in older adults. Therefore, identifying interventions that help to maintain cognitive function in older adults or that reduce the risk of dementia is a research priority. Cognitive training uses repeated practice on standardised exercises targeting one or more cognitive domains and may be intended to improve or maintain optimal cognitive function. This review examines the effects of computerised cognitive training interventions lasting at least 12 weeks on the cognitive function of healthy adults aged 65 or older and has formed part of a wider project about modifying lifestyle to maintain cognitive function. We chose a minimum 12 weeks duration as a trade-off between adequate exposure to a sustainable intervention and feasibility in a trial setting.

OBJECTIVES

To evaluate the effects of computerised cognitive training interventions lasting at least 12 weeks on cognitive function in cognitively healthy people in late life.

SEARCH METHODS

We searched to 31 March 2018 in ALOIS (www.medicine.ox.ac.uk/alois), and we performed additional searches of MEDLINE, Embase, PsycINFO, CINAHL, ClinicalTrials.gov, and the WHO Portal/ICTRP (www.apps.who.int/trialsearch), to ensure that the search was as comprehensive and as up-to-date as possible to identify published, unpublished, and ongoing trials.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs, published or unpublished, reported in any language. Participants were cognitively healthy people, and at least 80% of the study population had to be aged 65 or older. Experimental interventions adhered to the following criteria: intervention was any form of interactive computerised cognitive intervention - including computer exercises, computer games, mobile devices, gaming console, and virtual reality - that involved repeated practice on standardised exercises of specified cognitive domain(s) for the purpose of enhancing cognitive function; the duration of the intervention was at least 12 weeks; cognitive outcomes were measured; and cognitive training interventions were compared with active or inactive control interventions.

DATA COLLECTION AND ANALYSIS

We performed preliminary screening of search results using a 'crowdsourcing' method to identify RCTs. At least two review authors working independently screened the remaining citations against inclusion criteria. At least two review authors also independently extracted data and assessed the risk of bias of included RCTs. Where appropriate, we synthesised data in random-effects meta-analyses, comparing computerised cognitive training (CCT) separately with active and inactive controls. We expressed treatment effects as standardised mean differences (SMDs) with 95% confidence intervals (CIs). We used GRADE methods to describe the overall quality of the evidence for each outcome.

MAIN RESULTS

We identified eight RCTs with a total of 1183 participants. The duration of the interventions ranged from 12 to 26 weeks; in five trials, the duration of intervention was 12 or 13 weeks. The included studies had moderate risk of bias, and the overall quality of evidence was low or very low for all outcomes. We compared CCT first against active control interventions, such as watching educational videos. Negative SMDs favour CCT over control. Trial results suggest slight improvement in global cognitive function at the end of the intervention period (12 weeks) (standardised mean difference (SMD) -0.31, 95% confidence interval (CI) -0.57 to -0.05; 232 participants; 2 studies; low-quality evidence). One of these trials also assessed global cognitive function 12 months after the end of the intervention; this trial provided no clear evidence of a persistent effect (SMD -0.21, 95% CI -0.66 to 0.24; 77 participants; 1 study; low-quality evidence). CCT may result in little or no difference at the end of the intervention period in episodic memory (12 to 17 weeks) (SMD 0.06, 95% CI -0.14 to 0.26; 439 participants; 4 studies; low-quality evidence) or working memory (12 to 16 weeks) (SMD -0.17, 95% CI -0.36 to 0.02; 392 participants; 3 studies; low-quality evidence). Because of the very low quality of the evidence, we are very uncertain about the effects of CCT on speed of processing and executive function. We also compared CCT to inactive control (no interventions). We found no data on our primary outcome of global cognitive function. At the end of the intervention, CCT may lead to slight improvement in episodic memory (6 months) (mean difference (MD) in Rivermead Behavioural Memory Test (RBMT) -0.90 points, 95% confidence interval (CI) -1.73 to -0.07; 150 participants; 1 study; low-quality evidence) but can have little or no effect on executive function (12 weeks to 6 months) (SMD -0.08, 95% CI -0.31 to 0.15; 292 participants; 2 studies; low-quality evidence), working memory (16 weeks) (MD -0.08, 95% CI -0.43 to 0.27; 60 participants; 1 study; low-quality evidence), or verbal fluency (6 months) (MD -0.11, 95% CI -1.58 to 1.36; 150 participants; 1 study; low-quality evidence). We could not determine any effects on speed of processing because the evidence was of very low quality. We found no evidence on quality of life, activities of daily living, or adverse effects in either comparison.

AUTHORS' CONCLUSIONS

We found low-quality evidence suggesting that immediately after completion of the intervention, small benefits of CCT may be seen for global cognitive function when compared with active controls, and for episodic memory when compared with an inactive control. These benefits are of uncertain clinical importance. We found no evidence that the effect on global cognitive function persisted 12 months later. Our confidence in the results was low, reflecting the overall quality of the evidence. In five of the eight trials, the duration of the intervention was just three months. The possibility that more extensive training could yield larger benefit remains to be more fully explored. We found substantial literature on cognitive training, and collating all available scientific information posed problems. Duration of treatment may not be the best way to categorise interventions for inclusion. As the primary interest of older people and of guideline writers and policymakers involves sustained cognitive benefit, an alternative would be to categorise by length of follow-up after selecting studies that assess longer-term effects.

Computerised cognitive training for maintaining cognitive function in cognitively healthy people in late life

BACKGROUND

Increasing age is associated with a natural decline in cognitive function and is also the greatest risk factor for dementia. Cognitive decline and dementia are significant threats to independence and quality of life in older adults. Therefore, identifying interventions that help to maintain cognitive function in older adults or to reduce the risk of dementia is a research priority. Cognitive training uses repeated practice on standardised exercises targeting one or more cognitive domains and is intended to maintain optimum cognitive function. This review examines the effect of computerised cognitive training interventions lasting at least 12 weeks on the cognitive function of healthy adults aged 65 or older.

OBJECTIVES

To evaluate the effects of computerised cognitive training interventions lasting at least 12 weeks for the maintenance or improvement of cognitive function in cognitively healthy people in late life.

SEARCH METHODS

We searched to 31 March 2018 in ALOIS (www.medicine.ox.ac.uk/alois) and performed additional searches of MEDLINE, Embase, PsycINFO, CINAHL, ClinicalTrials.gov, and the WHO Portal/ICTRP (www.apps.who.int/trialsearch) to ensure that the search was as comprehensive and as up-to-date as possible, to identify published, unpublished, and ongoing trials.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs, published or unpublished, reported in any language. Participants were cognitively healthy people, and at least 80% of the study population had to be aged 65 or older. Experimental interventions adhered to the following criteria: intervention was any form of interactive computerised cognitive intervention - including computer exercises, computer games, mobile devices, gaming console, and virtual reality - that involved repeated practice on standardised exercises of specified cognitive domain(s) for the purpose of enhancing cognitive function; duration of the intervention was at least 12 weeks; cognitive outcomes were measured; and cognitive training interventions were compared with active or inactive control interventions.

DATA COLLECTION AND ANALYSIS

We performed preliminary screening of search results using a 'crowdsourcing' method to identify RCTs. At least two review authors working independently screened the remaining citations against inclusion criteria. At least two review authors also independently extracted data and assessed the risk of bias of included RCTs. Where appropriate, we synthesised data in random-effect meta-analyses, comparing computerised cognitive training (CCT) separately with active and inactive controls. We expressed treatment effects as standardised mean differences (SMDs) with 95% confidence intervals (CIs). We used GRADE methods to describe the overall quality of the evidence for each outcome.

MAIN RESULTS

We identified eight RCTs with a total of 1183 participants. Researchers provided interventions over 12 to 26 weeks; in five trials, the duration of intervention was 12 or 13 weeks. The included studies had a moderate risk of bias. Review authors noted a lot of inconsistency between trial results. The overall quality of evidence was low or very low for all outcomes.We compared CCT first against active control interventions, such as watching educational videos. Because of the very low quality of the evidence, we were unable to determine any effect of CCT on our primary outcome of global cognitive function or on secondary outcomes of episodic memory, speed of processing, executive function, and working memory.We also compared CCT versus inactive control (no interventions). Negative SMDs favour CCT over control. We found no studies on our primary outcome of global cognitive function. In terms of our secondary outcomes, trial results suggest slight improvement in episodic memory (mean difference (MD) -0.90, 95% confidence interval (CI) -1.73 to -0.07; 150 participants; 1 study; low-quality evidence) and no effect on executive function (SMD -0.08, 95% CI -0.31 to 0.15; 292 participants; 2 studies; low-quality evidence), working memory (MD -0.08, 95% CI -0.43 to 0.27; 60 participants; 1 study; low-quality evidence), or verbal fluency (MD -0.11, 95% CI -1.58 to 1.36; 150 participants; 1 study; low-quality evidence). We could not determine any effects on speed of processing at trial endpoints because the evidence was of very low quality.We found no evidence on quality of life, activities of daily living, or adverse effects in either comparison.

AUTHORS' CONCLUSIONS

We found little evidence from the included studies to suggest that 12 or more weeks of CCT improves cognition in healthy older adults. However, our limited confidence in the results reflects the overall quality of the evidence. Inconsistency between trials was a major limitation. In five of the eight trials, the duration of intervention was just three months. The possibility that longer periods of training could be beneficial remains to be more fully explored.

Computerised cognitive training for maintaining cognitive function in cognitively healthy people in midlife

BACKGROUND

Normal aging is associated with changes in cognitive function that are non-pathological and are not necessarily indicative of future neurocognitive disease. Low cognitive and brain reserve and limited cognitive stimulation are associated with increased risk of dementia. Emerging evidence now suggests that subtle cognitive changes, detectable years before criteria for mild cognitive impairment are met, may be predictive of future dementia. Important for intervention and reduction in disease risk, research also suggests that engaging in stimulating mental activity throughout adulthood builds cognitive and brain reserve and reduces dementia risk. Therefore, midlife (defined here as 40 to 65 years) may be a suitable time to introduce cognitive interventions for maintaining cognitive function and, in the longer term, possibly preventing or delaying the onset of clinical dementia.

OBJECTIVES

To evaluate the effects of computerised cognitive training interventions lasting at least 12 weeks for maintaining or improving cognitive function in cognitively healthy people in midlife.

SEARCH METHODS

We searched up to 31 March 2018 in ALOIS (www.medicine.ox.ac.uk/alois), the specialised register of the Cochrane Dementia and Cognitive Improvement Group (CDCIG). We ran additional searches in MEDLINE, Embase, PsycINFO, CINAHL, ClinicalTrials.gov, and the WHO Portal/ICTRP at www.apps.who.int/trialsearch, to ensure that the search was as comprehensive and as up-to-date as possible, to identify published, unpublished, and ongoing trials.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) or quasi-RCTs, published or unpublished, reported in any language. Participants were cognitively healthy people between 40 and 65 years of age (80% of study population within this age range). Experimental interventions adhered to the following criteria: intervention was any form of interactive computerised cognitive intervention - including computer exercises, computer games, mobile devices, gaming console, and virtual reality - that involved repeated practice on standardised exercises of specified cognitive domain(s) for the purpose of enhancing cognitive function; duration of the intervention was at least 12 weeks; cognitive outcomes were measured; and cognitive training interventions were compared with active or inactive control interventions.

DATA COLLECTION AND ANALYSIS

For preliminary screening of search results, we used a 'crowd' method to identify RCTs. At least two review authors working independently screened remaining citations against inclusion criteria; independently extracted data; and assessed the quality of the included trial, using the Cochrane risk of bias assessment tool. We used GRADE to describe the overall quality of the evidence.

MAIN RESULTS

We identified one eligible study that examined the effect of computerised cognitive training (CCT) in 6742 participants over 50 years of age, with training and follow-up duration of six months. We considered the study to be at high risk of attrition bias and the overall quality of the evidence to be low.Researchers provided no data on our primary outcome. Results indicate that there may be a small advantage for the CCT group for executive function (mean difference (MD) -1.57, 95% confidence interval (CI) -1.85 to -1.29; participants = 3994; low-quality evidence) and a very small advantage for the control group for working memory (MD 0.09, 95% CI 0.03 to 0.15; participants = 5831; low-quality evidence). The intervention may have had little or no effect on episodic memory (MD -0.03, 95% CI -0.10 to 0.04; participants = 3090; low-quality evidence).

AUTHORS' CONCLUSIONS

We found low-quality evidence from only one study. We are unable to determine whether computerised cognitive training is effective in maintaining global cognitive function among healthy adults in midlife. We strongly recommend that high-quality studies be undertaken to investigate the effectiveness and acceptability of cognitive training in midlife, using interventions that last long enough that they may have enduring effects on cognitive and brain reserve, and with investigators following up long enough to assess effects on clinically important outcomes in later life.

Computerised cognitive training for preventing dementia in people with mild cognitive impairment

BACKGROUND

The number of people living with dementia is increasing rapidly. Clinical dementia does not develop suddenly, but rather is preceded by a period of cognitive decline beyond normal age-related change. People at this intermediate stage between normal cognitive function and clinical dementia are often described as having mild cognitive impairment (MCI). Considerable research and clinical efforts have been directed toward finding disease-modifying interventions that may prevent or delay progression from MCI to clinical dementia.

OBJECTIVES

To evaluate the effects of at least 12 weeks of computerised cognitive training (CCT) on maintaining or improving cognitive function and preventing dementia in people with mild cognitive impairment.

SEARCH METHODS

We searched to 31 May 2018 in ALOIS (www.medicine.ox.ac.uk/alois) and ran additional searches in MEDLINE, Embase, PsycINFO, CINAHL, ClinicalTrials.gov, and the WHO portal/ICTRP (www.apps.who.int/trialsearch) to identify published, unpublished, and ongoing trials.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-RCTs in which cognitive training via interactive computerised technology was compared with an active or inactive control intervention. Experimental computerised cognitive training (CCT) interventions had to adhere to the following criteria: minimum intervention duration of 12 weeks; any form of interactive computerised cognitive training, including computer exercises, computer games, mobile devices, gaming console, and virtual reality. Participants were adults with a diagnosis of mild cognitive impairment (MCI) or mild neurocognitive disorder (MND), or otherwise at high risk of cognitive decline.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed risk of bias of the included RCTs. We expressed treatment effects as mean differences (MDs) or standardised mean differences (SMDs) for continuous outcomes and as risk ratios (RRs) for dichotomous outcomes. We used the GRADE approach to describe the overall quality of evidence for each outcome.

MAIN RESULTS

Eight RCTs with a total of 660 participants met review inclusion criteria. Duration of the included trials varied from 12 weeks to 18 months. Only one trial used an inactive control. Most studies were at unclear or high risk of bias in several domains. Overall, our ability to draw conclusions was hampered by very low-quality evidence. Almost all results were very imprecise; there were also problems related to risk of bias, inconsistency between trials, and indirectness of the evidence.No trial provided data on incident dementia. For comparisons of CCT with both active and inactive controls, the quality of evidence on our other primary outcome of global cognitive function immediately after the intervention period was very low. Therefore, we were unable to draw any conclusions about this outcome.Due to very low quality of evidence, we were also unable to determine whether there was any effect of CCT compared to active control on our secondary outcomes of episodic memory, working memory, executive function, depression, functional performance, and mortality. We found low-quality evidence suggesting that there is probably no effect on speed of processing (SMD 0.20, 95% confidence interval (CI) -0.16 to 0.56; 2 studies; 119 participants), verbal fluency (SMD -0.16, 95% CI -0.76 to 0.44; 3 studies; 150 participants), or quality of life (mean difference (MD) 0.40, 95% CI -1.85 to 2.65; 1 study; 19 participants).When CCT was compared with inactive control, we obtained data on five secondary outcomes, including episodic memory, executive function, verbal fluency, depression, and functional performance. We found very low-quality evidence; therefore, we were unable to draw any conclusions about these outcomes.

AUTHORS' CONCLUSIONS

Currently available evidence does not allow us to determine whether or not computerised cognitive training will prevent clinical dementia or improve or maintain cognitive function in those who already have evidence of cognitive impairment. Small numbers of trials, small samples, risk of bias, inconsistency between trials, and highly imprecise results mean that it is not possible to derive any implications for clinical practice, despite some observed large effect sizes from individual studies. Direct adverse events are unlikely to occur, although the time and sometimes the money involved in computerised cognitive training programmes may represent significant burdens. Further research is necessary and should concentrate on improving methodological rigour, selecting suitable outcomes measures, and assessing generalisability and persistence of any effects. Trials with long-term follow-up are needed to determine the potential of this intervention to reduce the risk of dementia.